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Re: [Xen-devel] [PATCH v2] xen: Implement hypercall for tracing of program counters

On 31/07/17 10:56, Wei Liu wrote:
On Mon, Jul 31, 2017 at 09:22:35AM +0100, Julien Grall wrote:

On 07/28/2017 04:37 PM, Wei Liu wrote:
On Wed, Jul 26, 2017 at 12:43:45PM +0200, Felix Schmoll wrote:
+        d->tracing_buffer = NULL;
+        if ( copy_to_guest(buf, temp, d->tracing_buffer_pos) )
+            ret = -EFAULT;
+        xfree(temp);
+        ret = d->tracing_buffer_pos;
+        break;
+    }
+    default:
+        ret = -ENOSYS;


Should not it be -EOPNOTSUPP to match return error when CONFIG_TRACE_PC is

AIUI EOPNOTSUPP means "This is a valid operation but I am not configured
to support it" while EINVAL means "This is an invalid value

Fair enough. However, you impose the caller to check -EINVAL and -EOPNOTSUPP in order to know if an operation can be done.

I first thought all the other hypercalls use -EOPNOTSUPP, but in face they use -ENOSYS. It would be to be consistent with the rest rather than reinventing our own.

Julien Grall

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